In daily life, there is a situation where a length such as a width or height of a space in which an object is placed is desired to be known. To deal with this, in the present circumstances, for example, a measure is used to measure the length in many cases, but for reasons that operation is troublesome, it is difficult to measure a length out of reach, and the like, it is requested to enable measurement easily in a non-contact manner. Further, a system is desired that allows, at the time of measurement, whether an intended portion of an object is being able to be measured to be visually identified easily. Thus, a technique has been proposed in which images that are captured from different viewpoints are used to acquire three-dimensional information such as a distance to an object or a length of the object from disparity information which indicates a shift between the viewpoints.
PTL 1 discloses a technique that by using an image capturing apparatus including two imaging units, a three-dimensional model of an object is generated from pair images having binocular disparity and a length between two points designated by a user is calculated, and it is possible to measure an actual length between the designated two points on the image.
Further, PTL 2 discloses a technique that, in the same manner as PTL 1, by using an image capturing apparatus including two imaging units, distance information is acquired from pair images having binocular disparity. In PTL 2, further, distance data which is measured partially on an observation plane is subjected to Hough transform, a plane is estimated by applying two or more straight lines within the observation plane, and distance information in the plane is acquired, thus making it possible to acquire undetermined distance data in the plane.